docs: def idx_infeasible(self, solution_genotype):
          """return indices of "infeasible" variables, that is,
          variables that do not directly map into the feasible domain such that
          ``tf.inverse(tf(x)) == x``.
  
          """
          res = [i for i, x in enumerate(solution_genotype)
                                  if not self.is_feasible_i(x, i)]
          return res